Process and apparatus for die-casting of ferrous metals

ABSTRACT

In a process for the production of die-cast ferrous metals, using refractory metal dies and moulds, the molten ferrous metal passes through a shot sleeve en route to the mould. The invention provides a continuous coating of an adherent, heat-insulating, refractory composition. Said composition comprises a finely divided refractory material, suspending and binding agents therefore, and a liquid media that will evaporate or be otherwise removed from the composition at high temperatures.

United, States atent 1 Jeanneret PROCESS AND APPARATUS FOR DIE- CASTING OF FERROUS METALS [75] Inventor: Jean Louis Jeanneret, Brecksville,

Ohio

[73] Assignee: Foseco International Limited, Birmingham, England 22 Filed: Sept. 3, 1971 21 Appl.No.: 177,844

Related U.S. Application Data [63] Continuation of Ser. No. 811,212, March 27, 1969,

abandoned.

[30] Foreign Application Priority Data Mar. 27, 19 8 Great Britain ..14,717/ 68 [52 U.S. Cl. ..164/72, l17/5.3, 164/267 {51] Int. Cl.......

..B22c 3/00 [58] Field of Search... ..164/14, 33, 72-74, 164/119, 121, 138,309,31631-8,267;

[5 6] References Cited UNITED STATES PATENTS 3,544,355 2 1970 On .Q ..164/72 x 2,426,988 9/1947 Dean ..117/5.3 3,230,056 1 1966 Arant et al ..117/5.3 x 3,164,871 1/1965 Haughton ..117/5.3 x 3,447,936 6/1969 Omitz ..117 5.3 x

Primary ExaminerJ. Spencer Overholser Assistant Examiner-John E. Roethel Attorney-Wolfe, Hubbard, Voit & Osann 57 ABSTRACT 8 Claims, No Drawings This is a continuation of application Ser. No. 81 1,212 filed March. 27, 1969, now abandoned. This invention relates to processes for the die-casting of ferrous metals and to refractory compositions for use in such processes and in analogous processes.

The die-casting of non-ferrous metals, such as copper, brass and the like, has long been practiced. However the method has not been applicable to ferrous metals for many and varied reasons. More recently however there has been proposed, for use in diecasting, moulds and dies formed of so-called refractory metals, of which the main examples are tungsten,

' tantalum, molybdenum and columbium. These materials, and alloys of them, have very high melting points, high strength and elasticity, low thermal expansion and good thermal conductivity, properties which render them particularly valuable for the purpose.

Further, it has been found to be possible even to diecast ferrous metals e.g. gray iron, with the aid of moulds and dies of such refractory metals. However the method in practice presents difficulties. It is necessary to prevent the east ferrous metal from sticking to the mould and it has been found that a thin layer of graphite on the surface of the mould serves greatly to reduce any tendency for sticking.

Whilst in theory it might have seemed desirable to establish as close a contact as possible between the molten metal and the mould walls to induce immediate cooling, it is found in practice that this tends to produce die-cast products of rather poor surface quality. An improvement can be achieved by providing that the cooling occurs more slowly, i.e. that the thermal shock applied to the molten metal is reduced. Thus it is possible to operate the system with the moulds pre-heated to a suitabletemperature or by applying a suitable heatinsulating refractory coating to the inner surface of the mould.

A further and serious difficulty which arises however is the tendency for the molten ferrous metal to become chilled in the so-called shot-sleeve, i.e. the sleeve through which the molten metal is injected by the plunger into the mould cavity. Premature cooling tends to the formation of hard carbides which may scratch the sleeve wall and jam the plunger.

- One proposal for overcoming this difficulty has been the introduction into the shot-sleeve of a thin lining of asbestos or refractory fiber paper. Some measure of success has been achieved by this method but the method is difficult to carry out in practice andhas important disadvantages. Thus it is generally possible only to cover the lower part of the sleeve onto which the metal will rest by gravity but during injection it will fill the whole sleeve at the mould end, the liners are difficult and time-consuming to introduce, there is danger of metal flowing between the paper liner and the sleeve wall and thereby chill; and unless precautions are taken, moisture may be retained in the asbestos paper liner and be slowly released during the operation as vapor, with a consequent tendency to blow the metal. Moreover the provision of asbestos paper liners involves substantial expense.

It has now been found possible to eliminate the use of an asbestos paper liner and thereby to avoid its disadvantages, by providing the shot sleeve with an internal coating of a highly refractory heat insulating composition.

The formulation of a composition for the purpose, however has proved difficult, since the requirements of the system are rigorous. In particular it has been found important, for the best results, to provide that the composition should be readily applied, should flow smoothly and easily over the shot-sleeve surface and be strongly adherent thereto, and should, of course, have the necessary high insulating and refractory characteristics to make it resistant to the shock of the molten ferrous metal, always at a very high temperature. Most preferably the composition should be capable of ready application by spraying and should be kept readily in a uniform dispersion or suspension in the carrier.

According to the present invention therefore, in a process for the die-casting of ferrous metals, using refractory metal dies and moulds wherein the molten ferrous metal passes through a shot sleeve en route to the mould, there is provided the step of applying to the surface of the shot sleeve which contacts the molten metal a continuous coating of an adherent heat-insulating refractory composition.

More particularly according to the present invention there are provided compositions for use in said process which comprise finely divided refractory material, suspending and binding agents therefor and a liquid medium which is evaporated or otherwise removed from the composition at high temperature.

Suitable soft finely divided refractory materials include asbestos, vermiculite, pyrophyllite, talc, diatomaceous earth and cork. It is important that these materials be softer than the material from which the plunger used in the casting is made in order to minimize wear on the plunger. These refractory materials should also have a low heat conductivity since insulation is the main function of the coating.

A certain amount of bond is desirable; and, in some cases, the light bond supplied by the coherence of the particles themselves is sufficient. However, additional adhesion may be achieved by the inclusion of bentonite, alkali-metal silicate, phosphates, colloidal silica and the like. Because of the high temperature involved, in-

organic binders are preferred.

To provide a coating which has excellent suspension properties and can be easily sprayed at a high concentration or Baume reading in order to minimize the amount of water-or other liquid mediums sprayed into the sleeve and consequently reducing the temperature drop thereof, a suspending agent and other additives can be used. Gelling agents such as bentonite will prevent hard packing of the refractory materials upon standing of the wash. To increase the viscosity of the water carrier or liquid medium used, polymers such as C.M.C. (carboxymethyl cellulose), E.C.M.C. (ethylcarboxymethylcellulose) gums and polysaccharides can be added.

Other beneficial additives that may be used are surfactants which will react on the particle surface charges, and, by repelling the refractory particles, will assist in the suspension. Calcium and aluminum sulfate were found to be beneficial as well as calcium oxide and some polyacrylamide resins such as Carbopol. Still further additives include soap to promote suspension, form insulating air bubbles in the coating and provide a certain degree of lubricity. A fungicide may also be incorporated if bacterial deterioration is a problem.

The liquid medium of the composition is conveniently water, but organic solvents such as the lower alcohols, e.g. isopropyl alcohol, may be used if desired and burnt off to leave the desired coating. The amount of such liquid medium is preferably such as to render the composition suitable for application by means of a spray gun.

To provide extra lubrication of the plunger during the shot cycle, the addition of a high temperature lubricant suchas graphite may be included by coating the shot sleeve. A graphite may also be included in a composition that is applied to the shot-sleeve surface itself. When it may be suitable to add such a lubricant in some circumstances, it should be appreciated that some increase in heat conductivity may be involved.

Specific compositions for use in the process of the present invention may contain the following ingredients in the proportions indicated:

insulating, soft refractories 30 to 100% (one or combination thereof) Binder to 70% Suspension agents, Surfactants 0 to 20% Swelling Clays Bentonite 0 to 70% Graphite 0 to 40% Soap Powder 0 to 2% Fungicide 0 to 2% The following are specific Examples of compositions which may be used in the process of the invention (percentages given are by weight):

The quantity of such compositions used should be enough to provide a continuous coating on the interior of the short-sleeve. The amount applied is not critical but obviously the minimum coating thickness is applied which will do the job.

The composition of Example 1 provides a thixotropic formulation with a built-in lubricant that can be sprayed at 60 to 70 Baume to provide a soft-slippery coating. Example 2 illustrates a combination of insulating refractory materials held together rather strongly by sodium silicate. This type of coating should in most instances be applied onto a lubricating primary film such as graphite.

By means of the process described herein the tendency for premature chilling of the molten ferrous metal in the shot-sleeve can be wholly eliminated and the disadvantages which flow from such premature chilling accordingly avoided.

I claim:

1. In a process for the die-casting of ferrous metals, using refractory dies and moulds, wherein, under the action of a plunger, the molten ferrous metal passes through a shot sleeve en route to the mould, the step of applying to the surface of the shot sleeve which contacts the molten metal a continuous coating composition comprising an adherent, finely divided heatinsulating refractory composition, said refractory composition being softer than the material from which the plunger is made and being selected from the group consisting of asbestos, vermiculite, pyrophyllite, talc, diatomaceous earth, cork, and a mixture thereof.

2. A die-casting apparatus for the die-casting of ferrous metals comprising a mould element and a shot sleeve through which, under the action of a plunger, molten metal passes en route to the mould, the said shot sleeve having a coating over that part of its surface which, in use, makes contact with molten metal, said coating being a continuous coating of an adherent, finely divided heat-insulating refractory composition which is softer than the material from which the plunger is made and being selected from the group consisting of asbestos, vermiculite, pyrophyllite, talc, diatomaceous earth, cork, and a mixture thereof.

3. A process according to claim 1 wherein the coating composition comprises a finely divided refractory material, at least one substance selected from suspending and binding agents therefor and at least one substance selected from volatile or combustible liquid media.

4. A process according to claim 3 wherein the binding agent is selected from the group consisting of bentonite, alkali metal silicates, phosphates, and colloidal silica.

5. A process according to claim 4 wherein the binding agent is bentonite.

6. A process according to claim 3 containing a surfactant.

7. A process according to claim 3 wherein the liquid medium is selected from the group consisting of water and isopropyl alcohol.

8. A process according to claim 3 wherein the composition comprises 30 to parts by weight of finely divided refractory material, up to 70 parts of a binder, up to 20 parts of a suspension agent, up to 40 parts of graphite, up to 2 parts of soap powder, and up to 2 parts of fungicide.

i I3 k 

2. A die-casting apparatus for the die-casting of ferrous metals comprising a mould element and a shot sleeve through which, under the action of a plunger, molten metal passes en route to the mould, the said shot sleeve having a coating over that part of its surface which, in use, makes contact with molten metal, said coating being a continuous coating of an adherent, finely divided heat-insulating refractory composition which Is softer than the material from which the plunger is made and being selected from the group consisting of asbestos, vermiculite, pyrophyllite, talc, diatomaceous earth, cork, and a mixture thereof.
 3. A process according to claim 1 wherein the coating composition comprises a finely divided refractory material, at least one substance selected from suspending and binding agents therefor and at least one substance selected from volatile or combustible liquid media.
 4. A process according to claim 3 wherein the binding agent is selected from the group consisting of bentonite, alkali metal silicates, phosphates, and colloidal silica.
 5. A process according to claim 4 wherein the binding agent is bentonite.
 6. A process according to claim 3 containing a surfactant.
 7. A process according to claim 3 wherein the liquid medium is selected from the group consisting of water and isopropyl alcohol.
 8. A process according to claim 3 wherein the composition comprises 30 to 70 parts by weight of finely divided refractory material, up to 70 parts of a binder, up to 20 parts of a suspension agent, up to 40 parts of graphite, up to 2 parts of soap powder, and up to 2 parts of fungicide. 